U.S. patent number 4,080,823 [Application Number 05/739,391] was granted by the patent office on 1978-03-28 for vibration measurement.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to Hans Stargardter.
United States Patent |
4,080,823 |
Stargardter |
March 28, 1978 |
Vibration measurement
Abstract
Apparatus and methods for measuring deflection of rotating fan
blades of a gas turbine engine is disclosed. The measurement of
bending and torsional deformation in response to integral and to
nonintegral vibration as well as to structural loading is
developed. Optical measuring techniques including the projection of
collimated light beams into the fan section of the engine are
employed. A linear readout of angular deflection is displayed on a
distant screen for amplification of the actual deflection. The
plurality of beams provide a deflection profile covering the full
surface of the blade.
Inventors: |
Stargardter; Hans (Bloomfield,
CT) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
24972068 |
Appl.
No.: |
05/739,391 |
Filed: |
November 5, 1976 |
Current U.S.
Class: |
73/655;
73/656 |
Current CPC
Class: |
G01H
1/006 (20130101); G01H 9/00 (20130101) |
Current International
Class: |
G01H
1/00 (20060101); G01H 9/00 (20060101); G01H
001/00 () |
Field of
Search: |
;73/67,67.2,71.3
;356/154,167 ;416/61 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
1082014 |
December 1913 |
Digby et al. |
2959956 |
November 1960 |
Sweeney et al. |
|
Foreign Patent Documents
|
|
|
|
|
|
|
1,446,960 |
|
Jun 1966 |
|
FR |
|
1,353,732 |
|
May 1974 |
|
UK |
|
Primary Examiner: Myracle; Jerry W.
Assistant Examiner: Beauchamp; John P.
Attorney, Agent or Firm: Walker; Robert C.
Claims
Having thus described typical embodiments of my invention, that
which I claim as new and desire to secure by Letters Patent of the
United States is:
1. Apparatus for measuring torsional and bending deflection in a
rotating blade of an operating rotary machine, comprising:
a plurality of reflecting surfaces spaced along the surface of the
blade to be measured;
means for directing a collimated beam of light energy into the path
of each reflecting surface so as to be reflected by each of said
surfaces at each machine revolution; and
a display screen spaced from the blade for intercepting the beams
reflected from the surfaces to display a composite pattern of the
multiple reflections which is representative of torsional and
bending deflection along the surface of the blade.
2. The invention according to claim 1 wherein said means for
directing a beam of light energy comprises an array of individual
light sources, each source being directed at an individual
reflecting surface.
3. The invention according to claim 1 wherein said means for
directing a beam of light energy comprises a single source of
collimated light energy and an array of beam splitters which are
adapted to direct a portion of the light energy emanated from said
collimated beam to each of the individual reflecting surfaces.
4. The invention according to claim 1 wherein each of said
reflecting surfaces is a diffraction grating and said means for
directing a beam of collimated light energy comprises a single
source of energy which is projected upon the diffraction
gratings.
5. The invention according to claim 1 wherein said means for
directing a beam of light energy is optically positioned behind
said screen and wherein said screen is formed to allow the passage
of said beam of collimated light energy therethrough.
6. The invention according to claim 5 wherein said screen has at
least one aperture disposed therein.
7. The invention according to claim 1 which further comprises
recording means disposed in operative relationship to said screen
for recording the composite pattern produced during operation.
8. The invention according to claim 2 which further comprises
recording means disposed in operative relationship to said screen
for recording the composite pattern produced during operation.
9. The invention according to claim 3 which further comprises
recording means disposed in operative relationship to said screen
for recording the composite pattern produced during operation.
10. The invention according to claim 1 wherein said screen is
positioned at approximately 20 feet from said reflecting
surfaces.
11. The invention according to claim 2 wherein said screen is
positioned at approximately 20 feet from said reflecting
surfaces.
12. The invention according to claim 3 wherein said screen is
positioned at approximately 20 feet from said reflecting
surfaces.
13. A method for measuring the angular deflection of a rotor blade
in a blade system subjected to nonintegral vibration, which
comprises the steps of:
disposing a plurality of reflecting surfaces along the span of the
blade on which deflection is to be measured;
rotating the blade system at an operational speed at which
nonintegral vibration is produced;
directing a beam of collimated light energy against each of said
reflecting surfaces;
reflecting said beam to a display screen to visually display the
pattern of reflected light energy produced in response to torsional
and bending deflection of the blade;
measuring the linear dimensions of the displayed pattern; and
relating the measured linear dimensions to angular deflection of
the blade.
14. A method for measuring the angular deflection of a rotor blade
in a blade system subjected to resonant vibration, which comprises
the steps of:
disposing a plurality of reflecting surfaces along the span of the
blade on which deflection is to be measured;
rotating the blade system at an operational speed just below the
speed at which peak resonant vibration is produced;
directing a beam of collimated light energy against each of said
reflecting surfaces;
reflecting said beam to a display screen to visually display a
first position of the reflected beam on the screen;
recording said first position of the reflected beam;
rotating the blade system at an operational speed just above the
speed at which peak resonant vibration is produced;
reflecting said beam to a display screen to visually display a
second position of the reflected beam on the screen;
recording said second position of the reflected beam;
determining the linear distance between said first and second
portions; and
relating said linear distance to angular deflection of the blade.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to deflection of blades in a rotary machine
and, more particularly, to methods and apparatus for measuring the
amplitude of deflection of operating blades.
2. Description of the Prior Art
Scientists and engineers within the turbine engine field have long
recognized that vibratory damage adversely limits the life of many
turbine machines. They have also recognized that the blades of the
rotor assembly are among the most susceptible of compressor
components to vibratory damage. The blades are of necessity
designed for low weight in order to minimize the centrifugallly
generated loads on the rotor. Lightweight blades, however, are not
always compatible with the durability requirements of the engine
and may severely limit the operating life of the engine where
adverse vibratory stimuli induce radical deflections in the
blades.
The frequency of the adverse stimuli may be an integral multiple or
a nonintegral multiple of the speed of the engine rotor is
revolutions per minute (RPM). Integral vibratory stimuli are
principally produced as a result of nonuniform pressure patterns
upstream of the blades. As each blade is cycled from a low loading
condition to a higher loading condition, the variation produced
causes the blades to cyclically deflect and a strain is imposed on
the blade material. One particularly distinctive form of integral
vibration is known as "resonance". At resonance, the natural
frequency of the installed blade is coincident with the frequency
of the stimuli. The deflection amplitudes become reinforcing and
the likelihood of vibratory damage is substantially increased.
Nonintegral vibration may occur at any speed and, in a most
destructive mode, is referred to in the industry as "flutter".
During flutter, self-excitation of the blades occurs as unsteady
forces and moments created by periodic blade deflections do
positive work on the blading. The periodic blade vibration may
consist of blade bending or torsion or a combination of the
two.
Structurally improved blade designs making judicious use of
material are possible where accurate measurement of blade
deflection enhances the understanding of vibratory effects.
Collaterally, the measurement of airfoil deformation in response to
gas pressure and centrifugal loadings enables improved aerodynamic
designs.
SUMMARY OF THE INVENTION
A primary aim of the present invention is to provide methods and
apparatus for optimizing the design of blades for a rotary machine,
such as a gas turbine engine. Accurate measurement of blade
deflections in response to structural and vibratory loads is sought
and, in one form, a specific object is to obtain optical
measurements which are representative of the deflection profile
over the full profile of the blade during steady state and
vibratory conditions.
According to the present invention, a plurality of reflecting
surfaces are positioned on a blade of a rotary machine so as to be
capable of intercepting a plurality of corresponding, collimated
light beams, and of directing said beams to a remotely positioned
viewing device to display a light pattern which is representative
of the torsional and bending deformations of the blade in response
to vibratory stimuli and structural loading.
A primary feature of the present invention is the plurality of
reflecting surfaces on the blade to be measured. Spanwise and
chordwise reflectors are employable. Another feature is the source
of collimated light which is adapted to direct light onto each
reflecting surface. The remotely positioned screen intercepts the
plurality of reflected beams to display a deflection pattern which
is representative of the blade profile under changing vibratory and
structural loadings.
A principal advantage of the present invention is the ability to
measure, with the apparatus and methods taught herein, blade
deflections in an operating machine. A profile of deflection of the
entire surface of the blade is obtainable. Deflections in response
to steady state loads and to both integral and nonintegral
vibration are measurable. Only minimal aerodynamic perturbations in
the flow path are produced as a result of the measurement
apparatus. The resulting optical pattern is amplifiable by
projecting the pattern to a remotely positioned screen. The
projected pattern represents the amplitude of both bending and
torsional deflections of the blade. Linear dimensions in the
pattern are convertible to angular deflections of the blade.
The foregoing, and other objects, features and advantages of the
present invention will become more apparent in the light of the
following detailed description of the preferred embodiment thereof
as shown in the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a simplified illustration of apparatus constructed to
employ the techniques of the present invention;
FIG. 2 is an alternate embodiment of apparatus constructed in
accordance with the present invention;
FIG. 3 is an alternate embodiment of apparatus constructed in
accordance with the present invention;
FIG. 4 is a simplified illustration showing the measurement of
torsional deflection amplitude of a blade in the first torsional
mode;
FIG. 5 is a simplified illustration showing the measurement of
bending deflection amplitude of a blade in the first bending
mode;
FIG. 6 is an illustration of combined bending and torsional
deflection amplitude measurement for nonintegral vibration; and
FIGS. 7A-7E are sequential illustrations of amplitude measurement
of resonant integral vibration.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Simplified apparatus for measuring torsional and bending deflection
in the fan blades of a gas turbine engine is illustrated in FIG. 1.
The gas turbine engine 10 is mounted on a frame 12. The fan blades
14 are viewable through the inlet 16 of the engine. One of the fan
blades has, on the surface thereof, a plurality of reflecting
surfaces 18. Each of the reflecting surfaces may be formed of a
mirror attached to the blades or may merely be a highly polished
piece of the blade itself.
A plurality of sources 20 of collimated light beams 22 are in
optical alignment with the reflecting surfaces 18. A display screen
24, having a plurality of apertures 26 in the embodiment shown
through which the beams 22 are transmittable, is disposed across
the path of the reflected beams. Optical viewing or recording means
28 is positioned relative to the screen to document the linear
representation of angular deflection as presented by the reflected
beams on the display screen. The viewing or recording means may be
any suitable means such as a still, movie camera or a
television-type display. Similarly, the display screen may be
formed of a diode array capable of digitizing the movement of the
intercepted light beam to provide a direct readout of deflection
amplitude.
In an alternate embodiment a single source 30 of collimated light
energy is aligned with a beam splitter 32. The beam splitter
intercepts and redirects a portion of the energy from the single
source to provide the plurality of light beams 22. As in FIG. 1,
the beams are reflectable from the surfaces 18 onto the screen 24.
Optical viewing or recording means 28 is positioned to document the
linear representation of angular deflection displayed on the
screen. As illustrated in the FIG. 2 embodiment, the screen may be
fabricated of a translucent material so as to make the projected
deflection profile pattern viewable from behind the screen.
Suitable viewing or recording means 28, such as a camera, may be
disposed behind the screen. As in FIG. 1, the display screen may be
formed of a diode array capable of digitizing the movement of the
intercepted light beam to provide a direct readout of deflection
amplitude.
Yet another embodiment of the invention is illustrated by FIG. 3. A
single source 30 of collimated light energy is aligned through an
aperture 34 in the fan case 36 with a plurality of diffraction
gratings 38. Each grating is adapted to direct light energy
striking the grating toward the screen 24. The angle of incidence
of the light energy striking the diffraction grating need not be
equal to the angle of reflection therefrom. The screen may be
fabricated of a translucent material so as to make the projected
deflection pattern viewable from behind the screen. Viewing or
recording means 28, such as a camera, may be disposed behind the
screen. As in FIGS. 1 and 2, the display screen may be formed of a
diode array capable of digitizing the light beam on the screen to
provide a direct readout of deflection amplitude.
In one embodiment the reflecting surfaces 18 are formed by mirrors
adhered to the blade 14. In an alternative embodiment local areas
of the parent blade material are polished to form integral
reflecting surfaces. In both embodiments only minimal aerodynamic
perturbations in the flow path are produced by the measurement and
accurate measurement is assured.
The measurement of deflection due to nonintegral vibration is
illustrated by FIGS. 4 and 5. A point image is produced on the
screen for each revolution of the engine as the reflecting surface
18 intercepts and reflects the light beam. In FIG. 4 torsional
deflection of the blade 14 causes linear displacement of the image
of the reflected beam 40 appearing on the screen 24. The locus of
image points displayed on the screen forms a horizontal line 42.
The additional three horizontal lines 44 shown on the screen of
FIG. 4 illustrate the loci of points formed by the reflections from
the three additional surfaces 18 disposed inwardly along the span
of the blade. Deflection in the first torsional mode is illustrated
although it will be clear to those skilled in the art that
deflection in other torsional modes may be similarly measured. The
length of the line 42 is proportional to the angular deflection of
the blade 14. The comparatively lesser lengths of the lines 44
illustrate lesser deflection inwardly along the span of the blade.
A blade deflection profile is thusly obtainable.
In FIG. 5 bending deflection of the blade 14 causes linear
displacement of the image of the reflected beam 40 appearing on the
screen 24. The locus of image points displayed on the screen forms
a vertical line 46. The additional three vertical lines 48 shown on
the screen 24 of FIG. 5 illustrate the loci of points formed by the
reflection from the three additional surfaces 18 disposed inwardly
along the span of the blade. Deflection of the blade in the first
bending mode is illustrated although it will be clear to those
skilled in the art that deflection in other bending modes may be
similarly measured. The length of the line 46 is proportional to
the angular deflection of the reflecting surface 18 carried by the
blade 14. The comparatively lesser lengths of the vertical lines 48
illustrate lesser deflections inwardly along the span of the
blade.
A composite representation of the torsional and bending deflections
of FIGS. 4 and 5 is illustrated on the screen 24 of FIG. 6. The
loci of points form a plurality of elipses as bending deflection
and torsional deflection vary in the operating blade system. In the
composite image the horizontal width A represents the maximum
torsional deflection and the vertical width B represents the
maximum bending deflection. The width of the minor axis of the
elipse varies with the phase differential between maximum torsional
deflection and maximum bending deflection. A slanted line image is
produced when the maximum torsional deflection and the maximum
bending deflection are in phase.
In forming deflection profiles at nonintegral frequencies, the
image shown on the screen represents the maximum amplitude of the
deflection in bending and in torsion. The technique for gauging the
maximum amplitude of deflection at resonant integral frequencies is
illustrated by FIGS. 7A-7E. The amplitude of deflection of the
blade in response to integral frequency stimuli remains constant as
a standing wave is developed in the blade system. Accordingly, the
image displayed on the screen 24 is a spot which may or may not be
representative of the maximum amplitude. In FIG. 7A a plot of the
amplitude of vibration as a function of engine RPM is shown. The
peak represents a precise resonant frequency at which deflection is
to be measured. Below the resonant frequency the amplitude of
vibration is small and a correspondingly small deflection is
measured on the screen 24. As the engine RPM is increased the
amplitude increases until just before the resonant frequency, the
displacement X as shown on the screen of FIG. 7C is at a maximum.
As soon as the engine RPM exceeds the resonant frequency the image
of the beam as displayed on the screen 24 moves abruptly to a
displacement X on the other side of the neutral axis. The excursion
of the intercepted beam as the system passes through resonance
defines a measurable linear displacement (2X) which is
representative of the deflection of the blade as excited by the
resonant vibration at the circumferential position illuminated.
Illumination at more than one circumferential position may be
required to locate and measure the maximum deflection. A timed
exposure photograph may be useful in measuring the 2X
displacement.
The optimum distance between the screen 24 and the reflecting
surfaces 18 is determined by the signal amplification desired. As
the distance between the screen and the surfaces is increased the
physical size of the image on the screen is proportionately
increased. It has been found that positioning the screen at a
distance of 20 feet from the surfaces produces an image on the
screen which is on the order of 6 inches and accurate measurement
is assured.
Steady state deflection in response to aerodynamic and centrifugal
loading is incorporated in the measurements of vibratory deflection
as described above. At engine RPM's intermediate to those producing
significant vibratory deflection, linear displacement of the
reflected light on the screen represents increased or decreased
deflection due to structural and aerodynamic loads. Accordingly, a
profile of the blade contour during operation may be developed and
the results applied to the design of new airfoils having improved
aerodynamic characteristics.
The apparatus disclosed is further useful in determining the
interblade phase angle between adjacent blades. A second blade is
equipped with reflecting surfaces and the angular lag in deflection
between the first and second blade is determined. The equipped
blades may be remote or adjacent with the phase lag calculated on
the basis of the number of blades in the system.
Although the invention has been shown and described with respect to
preferred embodiments thereof, it should be understood by those
skilled in the art that various changes and omissions in the form
and detail thereof may be made therein without departing from the
spirit and the scope of the invention.
* * * * *